100 Continue is sent even though Content-Length is not OK

[janderholm]

The following example which is a multipart upload with a maximum length set behaves in a way that I think is incorrect. I use commit a9fb5d6eb00ded502b021672779dd76c777680cd of warp which is recent on master

use warp::multipart::*;
use warp::Filter;

#[tokio::main]
async fn main() {
    let routes = warp::post()
        .and(warp::path("upload"))
        .and(warp::filters::path::full())
        .and(warp::multipart::form().max_length(1024 * 1024 * 10))
        .map(
            |full_path: warp::filters::path::FullPath,
             form_data: FormData| {
                 "Hello!"
             }
        );

    warp::serve(routes).run(([127, 0, 0, 1], 3030)).await;
}

Using this CURL command:
curl -vvv http://localhost:3030/upload/blergh.img -F file=@toolarge.bin

where toolarge.bin is larger than 1024 * 1024 * 10, I receive a "100 Continue" even though the header is not OK (content-length is too large).

> POST /upload/blergh.img HTTP/1.1
> Host: localhost:3030
> User-Agent: curl/7.52.1
> Accept: */*
> Content-Length: 11534536
> Expect: 100-continue
> Content-Type: multipart/form-data; boundary=------------------------808fc7c117e269f5
>
< HTTP/1.1 100 Continue
< HTTP/1.1 413 Payload Too Large
< content-type: text/plain; charset=utf-8
< content-length: 32
< date: Fri, 17 Jan 2020 12:53:41 GMT
* HTTP error before end of send, stop sending
<
* Curl_http_done: called premature == 0
* Closing connection 0
The request payload is too large

This confuses clients making them believe they should start sending data. And it causes issues when warp is placed behind a reverse proxy as the closed connection will make at least Apache respond with a 502 gateway error and swallow the error message passed by warp. Curl, and other clients, set the header Expect: 100-continue which indicate they want Content-Length to be verified before sending more data:

https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Expect

[janderholm]

I'm not sure my understanding of the behavior is entirely correct. What I do know is that placing a Warp server behind Apache as a reverse proxy will result in a 502 and a generic Apache error instead of the error returned by Warp.

[seanmonstar]

You're understanding is correct, this behavior happens in hyper due to it automatically responding with a 100 Continue no matter what. There's this issue regarding fixing that to only send the 100 Continue if the user tries to read from the body.

[seanmonstar]

This has been fixed in hyper v0.13.2, a cargo update should be all that's needed.